1. Field of the Invention
The present invention relates to a focus detector, and more particularly to a focus detector incorporated in an automatic focusing camera which has a plurality of focus-detecting regions. The present invention detects how a subject image is shifted from a reference position, and drives a photographing lens to a focusing position in accordance with the detection.
2. Description of the Related Art
Published Unexamined Japanese Patent Application No. 63-172209 discloses an automatic focus detector which is to be incorporated in an automatic focusing camera having a plurality of focus-detecting regions. In this automatic focus detector, a shift in the direction of the optical axis is corrected independently in each of the focus-detecting regions, such that focus detection can be performed with high accuracy even if a dimensional error in the direction of the optical axis exists between each light-receiving system and the optical system. More specifically, signals DTA to DTC output from the light-receiving systems are supplied to a first calculation section, by which the degrees of defocusing .DELTA..epsilon..sub.A, .DELTA..epsilon..sub.B and .DELTA..epsilon..sub.C are calculated. A second calculation section corrects these defocusing degrees as (.DELTA..epsilon..sub.A +.DELTA..epsilon..sub.AZ), (.DELTA..epsilon..sub.B +.DELTA..epsilon..sub.BZ) and (.DELTA..epsilon..sub.C +.DELTA..epsilon..sub.CZ), on the basis of the data which represents shifting degrees .DELTA..epsilon..sub.AZ, .DELTA..epsilon..sub.BZ and .DELTA..epsilon..sub.CZ detected in the direction of the optical axis, which data is stored in a memory beforehand. In this manner, a shifting degree in the direction of the optical axis is corrected independently with respect to each light-receiving system.
According to the publication, however, a shifting degree in the direction of the optical axis is corrected independently with respect to each focus-detecting region. This being so, the number of steps required for storing data on the shifting degrees will increase with an increase in the number of focus-detecting regions. In addition, a ROM having a larger storage capacity has to be employed. As a result, the manufacturing cost of the focus detector is inevitably high.